58 lines
2 KiB
C++
58 lines
2 KiB
C++
// Copyright (c) the JPEG XL Project Authors. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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#ifndef LIB_JPEGLI_HUFFMAN_H_
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#define LIB_JPEGLI_HUFFMAN_H_
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#include <stdint.h>
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#include <stdlib.h>
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#include "lib/jpegli/common_internal.h"
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namespace jpegli {
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constexpr int kJpegHuffmanRootTableBits = 8;
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// Maximum huffman lookup table size.
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// Requirements: alphabet of 257 symbols (256 + 1 special symbol for the all 1s
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// code) and max bit length 16, the root table has 8 bits.
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// zlib/examples/enough.c works with an assumption that Huffman code is
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// "complete". Input JPEGs might have this assumption broken, hence the
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// following sum is used as estimate:
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// + number of 1-st level cells
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// + number of symbols
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// + asymptotic amount of repeated 2nd level cells
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// The third number is 1 + 3 + ... + 255 i.e. it is assumed that sub-table of
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// each "size" might be almost completely be filled with repetitions.
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// Total sum is slightly less than 1024,...
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constexpr int kJpegHuffmanLutSize = 1024;
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struct HuffmanTableEntry {
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uint8_t bits; // number of bits used for this symbol
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uint16_t value; // symbol value or table offset
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};
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void BuildJpegHuffmanTable(const uint32_t* count, const uint32_t* symbols,
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HuffmanTableEntry* lut);
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// This function will create a Huffman tree.
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//
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// The (data,length) contains the population counts.
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// The tree_limit is the maximum bit depth of the Huffman codes.
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//
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// The depth contains the tree, i.e., how many bits are used for
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// the symbol.
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//
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// See http://en.wikipedia.org/wiki/Huffman_coding
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void CreateHuffmanTree(const uint32_t* data, size_t length, int tree_limit,
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uint8_t* depth);
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void ValidateHuffmanTable(j_common_ptr cinfo, const JHUFF_TBL* table,
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bool is_dc);
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void AddStandardHuffmanTables(j_common_ptr cinfo, bool is_dc);
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} // namespace jpegli
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#endif // LIB_JPEGLI_HUFFMAN_H_
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